The invention relates to a stretch-formable metal-plastic composite laminate, the use of the laminate and container therefrom.
It is known to use stretch-formed aluminum molded packs for pharmaceutical products and foodstuffs, for example as press-through packs, containers, under-seal trays, double molds and the like. They are able to meet to maximum effect the high requirements for the protection of the goods against diffusion of oxygen, steam and light, or escape of, for example fragrances, and to improve the user-friendliness of the pack.
In addition, sterilizability, pasteurizability or suitability for hot-filling often belong to the stated requirements.
The state of the art is to produce stretch-formed containers from laminates which have a central aluminum layer, an outer layer of oriented polyamide and an inner layer of polyvinyl chloride. Today the use of polyvinyl chloride should be limited due to reasons relating to environmental protection. Polyvinyl chloride-free layers or those low in polyvinyl chloride have the advantage that if they are energy-recycled as opposed to material-recycled, they produce no pollutants or only few pollutants on combustion. It is also advantageous for disposal and recycling of laminates of this type if there are as few as possible different types of material.
Composite laminates for packs containing no polyvinyl chloride are known per se.
European Application 0 317 818 describes a packaging laminate for tobacco products which has barrier properties. However, the material is only envisaged. for packing, for example cigarettes and is therefore very thin, that is having a maximum thickness limit of 2.5 mils, corresponding to 63.5 .mu.m. A material of this type is not suitable for stretch-forming.
U.S. Pat. Nos. 4,085,244 and 4,216,268 describe a laminated packaging film comprising an outer biaxially oriented polyamide film, a flexible metal foil, a biaxially oriented polypropylene and an inner sealing layer for the manufacture of pouches.
This film is less suitable as a stretch-form laminate because of its asymmetric construction with a relatively strong inner sealing layer. Furthermore, recycling is made more difficult by the use of two types of plastic.
German Patentschrift 3 436 412 describes a metal sheet laminated on one side or both sides with a biaxially oriented polyester film which ought to be suitable for drawing tins. To achieve secure bonding of metal to the polyester film, the metal sheet must have a double layer of hydrated chromium oxide. A metal sheet of this type is complex to manufacture and chromium oxide layers are undesirable, for example in foodstuffs packaging, or may be prohibited.
None of these film composites or laminates described hitherto can be combined to give optimum properties required for stretch-forming. This also applies to the properties required for reasons relating to environmental protection, which promote, for example recyclability of laminates or the objects prepared therefrom, such as packages.
A suitable composite laminate must support the stretching of the metal layer during the stretch-forming process, so that surface extensions of 80% and higher may be achieved without damage, such as perforation of the metal layer. Protection of the metal layer with regard to damage by cracks or perforation has greater significance since the metal layer serves primarily as a barrier layer against the diffusion of gases, such as oxygen, steam and light, and against the escape of fragrances and aromatic substances.